ABSTRACT:

Mila Field is located in the Sicily Channel, offshore Marina di Ragusa (fig. 1), in 60-70 metre water depth. Two appraisal wells (Mila 4 & Mila 6) were drilled in 1979 and 1984 through a 3.500 metre deep fractured limestone reservoir; the two wells were equipped with subsea completions and tight to a Floating Production Storage Offshore (FPSO), while a third well (Mila 5) was kept temporarily suspended, to be used as a future producer. The field was on stream till when the high water cut drove to the decision to stop the production and release the FPSO. Production data analysis and reservoir studies ended up with the request of the concession relinquishment. This paper reviews the planning and the operations carried out for the Plugging and Abandoning (P&A) of the three subsea wells in the years 2002-03.P&A operations were deemed critical because:

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    plugging of subsea wells have always been a non routine operation

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    the conditions of the subsea wells, shut in for more than 15 years, were uncertain

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    high pressure fluid was expected inside the completion strings due to the nature of the reservoir

Proper planning, including the development of contingency procedures, was the essential key for the success of the project. Isolations and barriers were designed to cope with all the contingencies. Safety and management systems were implemented and adhered to. First, it was decided to split the operations in two phases to perform the P&A program with the highest safety standard and the lowest cost:

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    The "Inspection Phase", to determine the status of the three wells and develop the program and the requirements for the second phase; these operations were performed in November 2002 with a moored diving barge.

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    The P&A Phase" these operations were performed with a floating rig to fully satisfy the contingency plan, in May / August 2003.

The project was successful:

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    Operation performed according to the highest safety standards

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    "Zero" accident

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    No hydrocarbon spillage

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    No time lost to overcome unplanned events

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    Final expenditure under budge

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